8/28/2011
y Plasticity: It is the measure of the moulding sand to flow
around and over a pattern during ramming and to uniformly fill the flask. y Collapsibility: This is the ability of the moulding sand to decrease in volume to some extent under the compressive p y g g g forces developed by the shrinkage of metal during freezing and subsequent cooling. y Adhesiveness: This is the property of sand mixture to adhere to another body (here, the moulding flasks). The moulding sand should cling to the sides of the moulding boxes so that it does not fall out when the flasks are lifted and turned over. This property depends on the type and amount of binder used in the sand mix. Compiled by: S K Mondal Made Easy
IES‐2008 Small amount of carbonaceous material sprinkled on the inner surface of mould cavity is called (a) Backing sand (b) Facing sand (c) Green sand (d) Dry sand Ans. (b)
Compiled by: S K Mondal Made Easy
IES‐2002 In the grain ‐size determination using standard charts, the relation between the given size number n and the average number of grains 'N' per square inch at a magnification of 100 X is (a) N = 2n (b) N = 2n‐l (c) N = 2n + 1 (d) N = 2n + 1
Other Sands y Facing sand: The small amount of carbonaceous
material sprinkled on the inner surface of the mold cavity to give a better surface finish to the castings. y Backing sand: It is what constitutes most of the refractory material found in the mould. mould This is made up of used and burnt sand. y Green Sand: The molding sand that contains moisture is termed as green sand. The green sand should have enough strength so that the constructed mould retains its shape. y Dry sand: When the moisture in the moulding sand is completely expelled, it is called dry sand. Compiled by: S K Mondal Made Easy
Grain size number y ASTM (American Society for Testing and Materials)
grain size number, defined as n-1 N 2 y Where N is the number of grains per square inch visible in a prepared specimen at 100X and n is the ASTM grain‐size number. Low ASTM numbers mean a few massive grains; high numbers refer to many small grains.
Compiled by: S K Mondal Made Easy
Casting Yield The casting yield is the proportion of the actual casting mass, w, to the mass of metal poured into the mould, W, expressed as a percentage.
Casting yield =
w × 100 W
Ans. (b) Compiled by: S K Mondal Made Easy
Compiled by: S K Mondal Made Easy
12